Porphyromonas gingivalis (Pg) is a Gram-negative anaerobe, strongly implicated in the etiology of adult periodontal disease. This research will increase our understanding of the molecular mechanisms that control synthesis of Pg cell surface glycans, and determine how changes in synthesis relate to biofilm persistence and pathogenicity. Our overarching model is that the biofilm state acts as a reservoir of bacteria, while capsule synthesis is linked to a transition to virulence and disruption of homeostasis. We have discovered that DNABII family members in Pg (HU PG0121 and HU PG1258) are involved in controlling synthesis of this surface polysaccharide. DNABII proteins are members of the Nucleoid Associated Proteins (NAPs), a class of proteins that possess multiple functions in maintaining the structure and function of DNA and RNA and are known to be critical for regulation of cell metabolism, the response to environmental perturbations, and in controlling the transition to and from a quiescent state. We have also identified an antisense RNA encoded in the 5'-end of the capsule locus (PG0104-PG0121) within a large 77bp inverted repeat (77bpIR) element. Deletion or over- expression of the region encoding this asRNA alters the synthesis of both LPS and K-antigen capsule. Our working model is that DNABII proteins interact with this asRNA and control expression of both the sense and antisense transcripts in this region. We have designated the asRNA asSuGR, for antisense Surface Glycan Regulator. The central hypothesis of this project is that HU PG0121 and HU PG1258 are key NAPs that play a fundamental role in modulating Pg pathogenicity. In these studies we will determine how these proteins and the 77bpIR element control synthesis of capsule and LPS. Our overall goal is to identify regulatory pathways that control the switch from a persistent, surface-attached state as a commensal to a virulent state capable of disrupting microbe-host homeostasis. The research proposed in this application is significant because understanding the control of surface property changes is a vital link to understanding the switch this commensal makes to a virulent pathogen. As an outcome of these studies, we will have characterized regulatory mechanisms that control the synthesis of surface glycans, key virulence determinants. This information will lead to a better understanding of the regulatory networks that either direct P. gingivalis to become a virulent pathogen or to continue to lie low and persist. Our results will potentially lead to the development of new therapeutic strategies for modulating biofilm formation by this oral pathogen.